Suboptimal cognitive functioning in Tyrosinemia I despite treatment?

A cross-sectional study was performed by Bendadi et al. to assess the cognitive functioning of children with tyrosinemia type I under treatment (with nitisinone and protein-restricted diet) compared with their unaffected siblings. Intelligence was measured using age-appropriate Wechsler Scales.

Average total IQ score in 10 patients with tyrosinemia type I receiving nitisinone was significantly lower compared with their unaffected siblings (71 ± 13 vs 91 ± 13; P = .008). Both verbal and performance IQ subscores differed significantly between the two groups.

Moreover, repeated IQ measurements in a single-center subset of 5 patients revealed a decline in average IQ score over time (P < .001).

No significant association was found between IQ score and either plasma tyrosine or phenylalanine concentration.